The Comparative Organismal Energetics Core (COEC) provides specialized expertise in the use of animal models, methodologies, and state-of-the-art instrumentation to facilitate energetics and aging research. The COEC provides a unique resource for investigators, with capabilities to perform complete energy budget analysis under environmental conditions of the users' choosing. The core is ideally suited to measure energy acquisition, storage, and utilization in a variety of animal models including C. elegans, Daphnia, Drosophila, Zebrafish, and rodents, and synergizes nicely with the overall mission of the UAB Nathan Shock Center (NSC). Interactions with the other Cores in the UAB NSC will be extensive. The Specific Aims of the Core are: 1. To provide expertise in the area of energetics and body composition in comparative animal models of aging; 2. To provide state-of-the-art instrumentation and methodology for the determination of body composition across the lifespan (dual energy X-ray absorptiometry, quantitative magnetic resonance, and micro- computed tomography); 3. To provide state-of-the-art instrumentation and methodology for the determination of energy balance across the lifespan (food intake, energy expenditure, and activity); 4. Develop new methodologies for assessing energetics/body composition in novel organisms. 5. Provide education and training on procedures and pitfalls in comparative organismal energetics (both internal and external to UAB)